LINQ将DateTime转换为字符串

Question

List<Post> list =
(
    from c in db.TitleComments
    join t in db.Titles on c.TitleId equals t.Id
    join u in db.Users on c.UserId equals u.Id
    where t.Id == _titleId && c.Date > time
    orderby c.Date descending
    select new Post { Username = u.Username, PostingDate = c.Date.ToString(), Data = c.Comment }
).ToList();

上面的代码导致date转换为string,PostingDate = c.Date.ToString().任何想法如何解决这个问题？

异常错误:{"LINQ to Entities无法识别方法'System.String ToString()'方法,并且此方法无法转换为商店表达式."}

Answer 1

linq试图使用sql将日期转换为字符串,但由于sql中没有ToString()方法它无法转换它,这种行为是设计的 - Joakim

换句话说,返回日期本身并在SQL端执行后将其转换为字符串:

(
select new { Username = u.Username,
    PostingDate = c.Date
    [...]
})
.ToList() // runs on SQL and returns to the application
.Select(o =>  // is not generating a SQL, it is running on the app
    new Post { Username = o.Username,
        PostingDate = o.PostingDate.ToString(),
        [...]
    })